781052 - IonMonkey: Impossible type in TypeSet in tight 3d-raytrace loop.

Status: RESOLVED INVALID

(Core :: JavaScript Engine, defect)

Description

[Sean Stangl [:sstangl]]

In SS-1.0's 3d-raytrace, Scene.prototype.intersect() begins with the following loop:

> var closest = null;
> for (i = 0; i < this.triangles.length; i++) {
>     var triangle = this.triangles[i];
>     var d = triangle.intersect(origin, dir, near, far);
>     if (d == null || d > far || d < near)
>         continue;
>     far = d;
>     closest = triangle;
> }

The comparisons are currently emitted as, respectively: LIsNullOrUndefined, LCompareV, and LCompareV.

At the first LCompareV, the TypeSets contain the following:

> lhs: Double, Int32, Null
> rhs: Double, Int32, Null, Undefined

However, it is impossible for |d|, |far|, or |near| to ever be Null at those locations. This prevents us from lowering the MCompare as LCompareD, which would be significantly faster.

Comment 1

[Brian Hackett [Laid off!]]

Bug 824257 added some stuff for eliminating type barriers when they are only filtering out an impossible null/undefined value.  I don't know how much of that logic can be reused here but the problems are similar.

Comment 2

[Jan de Mooij [:jandem]]

TypeSets no longer exist.